Gordy the gorilla got up and had a nice breakfast at the Como Park Zoo on April 19. He was fine when zookeepers looked in on him at 9:40 a.m., but when they returned 15 minutes later, he was dead.

It turns out Gordy died from heart disease, according to an autopsy completed by the University of Minnesota. His death is part of a disturbing trend among captive gorillas in North America who have developed progressive cardiovascular problems. Often, the deaths are sudden.

"Gordy's death was a shock," said Joanne Kelly, senior zookeeper at Como. "Our immediate assumption was it was his heart because it was so sudden."

Experts say 40 percent of captive gorilla deaths since 1980 -- recorded at zoos from San Francisco to Memphis to Washington, D.C. -- were caused by heart disease. The majority were males, especially those older than 30.

"It's unfortunate any time we lose one of these guys because they're so charismatic and engaging," said Dr. Tom Meehan, vice president of veterinary services at the Chicago Zoological Society.

Meehan was a lead researcher on a landmark study in the mid-1990s that brought the number of heart disease-related deaths to light. Zoos across America have been looking for answers since.

Schroeder, 24, in the back, and Togo, 21, are the two remaining gorillas at Como Zoo. Gordy’s death has been hard on zoo visitors, the zookeepers and the gorillas themselves.

The Gorilla Health Project, based in Cleveland, is a collaboration of experts who are trying to figure out why the disease is increasing and are working toward prevention. Gorillas have been given cardiac tests and zoos have submitted the results to a database to see if patterns can be determined.

"We're not concerned that this is a problem that will threaten the population, but it's our responsibility to care for the members of the population," Meehan said.

Researchers have yet to come up with an answer. Is it diet? Stress? Genetics? Infection?

There are medications, surgeries -- even implantable devices -- that are being used to treat gorillas diagnosed with heart problems.

One of the common forms of heart disease in gorillas is myocardial fibrosis, which is a hardening of the heart muscle. Gordy had it, according to the autopsy. He also had artherosclerosis, hardening of the arteries, which isn't as prevalent in gorillas but is a common cause of sudden death in adult humans.

Meehan said discussions have started about other species, such as chimpanzees and orangutans, to see if there are similar trends. Lessons learned from the gorilla project could be applied, he said.

Gordy, who was 23 when he died, was a western lowland gorilla, the only kind kept in zoos.

There were more than 100,000 western lowland gorillas in western Africa a decade ago, but in 2008 they were deemed "critically endangered" by the International Union for Conservation of Nature. Some estimates now put the population as low as 30,000 in the wild. Habitat destruction, poaching and disease are some of the threatening factors.

Problem is, Meehan said, there hasn't been much study of the wild gorillas, so it's hard to know if heart disease is common in them, too.

More than 360 gorillas live in 52 zoos across North America. Como is the only zoo in Minnesota with gorillas.

In the wild, gorillas might live into their 30s. In captivity, they can live past age 50.

"It's not enough to say the population is doing well in zoos or that they're living much longer," Meehan said. "You really want to take good care of each animal."